1. Field of Invention
The present invention relates to a field of permanent magnetic materials, and more particularly to a double-alloy NdFeB (neodymium-iron-boron) rare earth permanent magnetic material and a manufacturing method thereof.
2. Description of Related Arts
Because of the superior magnetic property, NdFeB rare earth permanent magnetic materials are widely applied on medical nuclear magnetic resonance imaging, hard disk drives, speakers, mobile phones, etc. And with the requirements of energy-saving and low-carbon economy, the NdFeB rare earth permanent magnetic materials are also applied on fields such as automobile parts, household appliances, energy-saving, control motors, hybrid cars and wind power generations.
In 1982, Japanese patents 1,622,492 and 2,137,496 about NdFeB rare earth permanent magnetic material were published by Japan Sumitomo Special Metals Co., Ltd. Then the company applied for United States patent and European patent. The patents disclosed the features, components and manufacture method of the NdFeB rare earth permanent magnetic material. The patents also disclosed the main phase: Nd2Fe14B phase, and the grain boundary phase: Nd-rich phase, B-rich phase and rare earth oxide impurities Almost at the same time, American GM Company applied for a very similar patent, U.S. Pat. No. 4,851,058. The difference of the two patents is the manufacturing method. The Japan Sumitomo Special Metals Co., Ltd. utilizes powder metallurgy technology, and the American GM Company utilizes melt spinning manufacturing method, wherein the method comprises producing powders at first, and then hot pressing the powder or mixing the powder with resin for producing magnet. The Japan Sumitomo Special Metals Co., Ltd. applied for patent U.S. Pat. No. 5,645,651 in July, 1995. Japan Santoku Metals Co., Ltd. obtained United States patent U.S. Pat. No. 5,383,978. The above are early patents of NdFeB.
Japan Hitachi Metals Co., Ltd. was incorporated with Japan Sumitomo Special Metals Co., Ltd. in Apr. 1, 2007 and the rights and duties of the NdFeB rare earth permanent magnetic material patent were inherited. When the Japan Hitachi Metals Co., Ltd. took legal action against the United States International Trade Commission (ITC), proprietary rights of the U.S. Pat. No. 6,461,565, U.S. Pat. No. 6,491,765, U.S. Pat. No. 6,537,385 and U.S. Pat. No. 6,527,874 were claimed.
Patent U.S. Pat. No. 6,461,565, filed May 8, 2011, whose Chinese application number is CN 1195600C, claims that magnetic compaction cannot be provided in protective gas, and applied for the protection of magnetic field generation under atmospheric conditions, wherein a working temperature is higher than 5° C. and lower than 30° C., a relative humidity is between 40% and 65%. Powder pressing is provided under the conditions. A sintering process appears after the pressing.
The scopes of the patent U.S. Pat. No. 6,491,765, filed May. 9, 2011 and the patent U.S. Pat. No. 6,537,385, filed Jul. 9, 2001 are almost the same. And the two patents applied for a same Chinese application CN 1272809C. The patent divides the powder production into two steps: the first step provides coarsely pulverization to alloy slices by hydrogen pulverization method; the second step provides finely pulverization by an inactive gas jet mill with oxygen content of 0.02˜5%. The products are collected by cyclone collector in such a manner that at least a part of the fine powder with a diameter less than 1 μm is removed and the content thereof is under 10% of the amount of the powder. In fact, all jet mills utilize cyclone collectors and emission of a part of the particles with a diameter less than 1 μm with the air flow is inevitable.
The patent U.S. Pat. No. 6,527,874 of the Japan Hitachi Metals Co., Ltd., filed Jul. 10, 2001, and the Chinese patent CN 1182548C claimed a strip casting technology in a smelting procedure of NdFeB rare earth permanent magnetic alloys made of metals selected from the group consisting of Nb and Mo. The Japan Sumitomo Special Metals Co., Ltd. invented the technology of producing sintering magnetic alloy by strip casting, which was authorized as patent JP 4,028,656, and patent U.S. Pat. No. 5,383,978 in January, 1995 in America. Then the technology was authorized as European patents EP 0,556,751B1 and EP 0,632,471B1.